April, 1963
RADIATION CHEMIS'TRY OF HIGHER A L i m a T I c ALCOHOLS
831
THE RADIATION CHEMISTRY OF SORI'E OF THE HIGHER ALIPHATIC ALCOHOLS-FURTHER STUDIES ON RADICALS TRAPPED A T LOW TERIPERATURESl BY RUSSELL H. JOHYSEN AND D. A. BECKER~ Department of Chemistry, Florida State University, Tallahassee, Florida Received September 21, 1962 The radiation chemistry of iso-propyl alcohol, 1-butanol, see-butyl alcohol and t-butyl alcohol has been investigated in both liquid and solid states. The effect of bleaching with visible and ultraviolet light on free radicals trapped in the low-temperature alcohol samples has been studied. The results of these experiments have been interpreted in terms of ionic and free radical reactions and applied to the problem of alcohol radiation chemistry in geneml.
Introduction I n an earlier studya the radiation chemistry of methanol, ethanol, and 1-propanol a t 25' and a t liquid nitrogen temperatures was investigated. This study was especially concerned with the nature of the paramagnetic species trapped in the low-temperature solids and the decomposition of these by the action of ultraviolet and visible light. It was concluded on the basis of these experiments that the principal products of irradiation are the alcohol radicals formed by the removal of an a-hydrogen and hydrogen. The alcohol radicals subsequently react to produce glycol and aldehyde in the absence of bleaching. Illumination of the glassy solid with light below 3000 8. results in the photolysis of these radicals with the production of smaller stable molecules such as methane, carbon monoxide, anid additional hydrogen. In the present work we have extended this type of investigation to some of the higher members of the homologous series and their structural isomers, with the view of studying particularly the effect of structure on photolytic behavior.
TABLE I GASEOUSRADIOLYTIC PRODK-CTS FROM Conditions of irradiation
--------I00 G(H2)
Experimental Results The results of these experiments are displayed in Tables 1-VIII. Theexperiments labeled "liquid (25°)"4 refer to experiments carried out at, room temperature but under the same conditions of geometry and radiation flux as those carried out at lower temperatures. Those samples labeled "solid (- 196')'' were allowed to melt in the dark and reach room temperature prior to analysis. Samples labeled "solid (- 196") visible bleach" were held at - 196' in a quartz dewar and ex(1) This work was supported i n part by the U. S. Atomio Energy Cammission under Contract AT-(40-1)-2001. (2) Abstracted in part from the M. 8. thesis of D. A. Becker, Florida State University, June, 1961. Presented before the Second International Congress of Radiation Research, Harrogate, England, August, 19G2. (3) R. H. Johnsen, J. P k y s . Ckem., 66, 2144 (1961). (4) &Butyl alcohol was irradiated a t 50" to maiatain the liquid oondition.
e.v. Yields---G(CH4) G(C0) G(CrC8)
Liquid (25") 3.74 1.53 0.19 3.63 .78 .06 Solid ( - 196') 4.34 .99 .12 Solid ( - 196') Visible bleach 15.61 1.53 .77 Solid ( - 196") Ultraviolet bleach" a Yield based on y-ray energy absorbed.
Total dose, e.v./g.
0.51 .62 .72
1 x 1019 1 X 1019 1 X 10lg
4.50
1 X 1019
TABLE I1 GASEOUS RADIOLYTIC PRODUCTS FROM BUTANOL Conditions of irradiation
----100 G(Hz)
e.v. Yields---G(CH4) G(C0)
4.18 0.10 0.08 Liquid (25') .20 .36 Solid (-196') 3.54 Solid (-196') 3.37 .i4 .yo Visible bleach Solid ( - 196") 18.40 .75 4.05 Ultraviolet bleach" a Yield based on y-ray energy absorbed.
Experimental Irradiation, analytical procedures, and dosimetry were identical with those described in the preceding paper, with the exception that glvcols were determined using vapor fractometry, as well aR by the periodic acid method. A %-centimeter CarhoWax-400 column operated a t 210", and a helium flow rate of 54 ml./min. was employed in these determinations. Total dosages are indicated in connection n i t h the experimental data. The alcohols employed in these studies mere purified by first drying over appropriate drying agents followed by fractional distillation. Samples were then transferred to the vacuum line where they were subjected to three bulb-to-bulb distillations prior to distillation into the irradiation vessels. In every case sample boiling over a one degree (or less) range was employed.
ISOPROPYL ALCOHOL
G(Cd
Total dose, e.v./g.
0.65 .18 .34
1 X lOl9 1 X 1OlD I x 1019
5.01
1 X lOl9
TABLE I11 GASEOKS RADIOLYTIC Conditions of irradiation
PRODKCTS FROI\I
7-----100
G(Ha)
8ec-Brn"r ALCOHOL
e.v. Yields-G(CH4) G(C0)
Liquid (25") 2.56 0.51 0.64 Solid (-196') 2.62 .32 .20 Solid ( - 196') 2.82 .40 .28 Visible bleach Solid (-196") 7.67 .89 2.15 Ultraviolet bleach" a Yield based on y-ray energy abporbed.
G(Cd
Total dose. e.v./g.
2.40 1.44 1.52
1 X 10lg 1 X lOI9 1 X 1019
3.97
1 X 1019
TABLE IV GASEOCSR A D I O L Y T I C Conditions of irradiation
PRODUCTS FROM t-BGTYL ALCOHOL
_---G(Hd
100 e.v. Yields----G(CH4) G(C0)
Liquid (30") 0.97 2.98 0.5.5 Solid ( - 196') 1.33 1.00 .1S Solid ( - 196') 1.45 1 . 2 1 .20 Visible bleach 1.52 0.29 .81 Solid (-196') Ult,raviolet blea ch" Yield based on y-ray energy absorbed.
G(Cd
Total dose. e.v./$.
2.91 2.06 1.24
1 X lOI9 1 X IOl9 1X
6.84
1 X 1019
posed to a 100-watt fluorescent lamp for one hour prior to melting. The "solid (- 196') ultraviolet bleach" samples were treated in the same manner except that the unfiltered output of an AH-6 mercury arc lamp was
RUSSELL€1. JOHNSEN AKD D. A. BECKER
832 TABLE V
Vol. 67
pointed out previously, considerable scatter in the data is observed when crystalline samples are used. Bleach100 0.v. Yields ing is especially difficult due to scattering of light from --Condition-------the opaque crystalline mass of the sample, and there is Solid Solid (-196') Liquid considerable doubt as to the effectiveness of the bleachl'ruduot (250) ( - 196') ultraviolet ing agents in this case. bleaoh Analyses of the gaseous products from liquid irradiaIsopropyl ether 0.10 0 02 0 Other ether .15 .06 0 tion are generally reproducible to 1%. For the solid Acetaldehyde .30 .13 0 irradiation this is reduced to around 5%. Analyses for Acetone 1.47 1.57 2.04 major liquid products mere reproducible to a like degree, Water trace trace 1.41 but for minor products this reproducibility was coiiGlycol .20 trace trace siderably reduced. Total dose, e.v./g. 13 X 1020 9 X 1020 8 X 1020 Discussion of Results TABLE1'1 Two major differences are to be noted when the reCONDESSED PRODUCTS FROM I-BCTAXOL RADIOLSSIS sults for the substances studied in the present work are 100 e.v. Yields compared with those reported earlier. First of all, the ---Condition------. yields of glycol are considerably reduced in relative Solid ( - 196") importance, and, secondly, the simple relationships Liquid Solid ultraviolet Product (250) (-196') bleach that were to be found among the radiolysis and photoButyraldehyde 0.62 1.24 1.89 lytic products from the lower alcohols are apparent only Formaldehyde 1.44 0 0 for the normal and secondary butanol cases. The more Ethanol 1.47 .35 .35 complicated relationships can largely be understood 1-Propanol 0.25 .ll .81 in terms of the increased molecular complexity which Water .37 .23 .54 results in a wider variety of possible decomposition Glycol .10 trave trace products, higher steric requirements for radical-radical Total dose, e.v./g. 4 x 1020 8 X lozo 12 X loz0 interactions, and the absence (except for 1-butanol) of the primary-CHOH grouping which seems particularly TABLE VI1 susceptible to photolytic decomposition. PRODUCTS FROM sec-BrrYL h C O H O L RADIOLYSIS COKDESSED A. Radiation Decomposition of Liquid Alcohols. 100 R . V . Yields (i) Caseous Products.-All of these alcohols have ConditionSolid ( - 196O) been previously studied by McDonnell and Newton5 Liquid Solid ultraviolet using 28 hlev. helium ions. Irradiation by X-rays Product ( - 196') bleach (250) results in a comparative increase in the hydrogen yield Acetaldehyde 0.46 0 24 0.21 ranging from 63.5 to 16.5y0 in the normal series from Propionaldehyde .09 .07 .06 methanol to 1-butanol. In the case of secondary and Acetone .l5 ,26 .28 t-butyl alcohol the hydrogen yields are lower (but only Methyl ethyl ketone .42 .94 3.66 slightly) than those reported by AlcDonnell and KewEthanol 0 0 03 0 Water trace trace trace toil using helium ions. These results would seem to Glycol . 1 (2) 0 0 suggest that the recombination of hydrogen atoms in Total dose, e.v./g. 5 x 1020 8 x 1020 8 x 1020 the track of the ionizing particle is a relatively uiiimportant mode of hydrogen formation in the liquid TABLE VI11 state. It should also be noted that there is no regular Coi~.u~~usrnu PRouLrcrs P'RORI t-BuwL ALCOHOLRAUIOLYSI~ change in the hydrogen yield as one goes to alcohols of 100 e.v. Yields higher molecular weight. This is true of both the X----Condition-------rays and helium ion studies, a secondary maximum Solid ( - 196') Liquid Solid ultraviolet bleach being present for 1-butanol in both studies. Product (25C) ( - 196O) Methane yields are uniformly higher for the X-ray Ether 0 17 0 03 0 03 case, as are the yields of the Cz-C4hydrocarbons. This Unidentified .ll .22 .19 suggests that reactions leading to products of higher L4cetone 1 08 91 2 17 molecular weight than these occur with greater fresec-Butyl alcohol 0.16 .12 0 16 quency in the higher L.E.T. case than here. Water 26 1 15 81 (ii) Liquid Products.-In Table IX the yields of Glycol trace 0 0 carbonyl compounds and glycols for six alcohols studied Total dose, e.v./g. 9 X loz0 7 x lozo 8 X loz0 in this Laboratory are juxtaposed with the results of lJlcDonnel1 and Newton6 in order more clearly to illusemployed as the bleaching agent. In the case where trate a rather unexpected linear energy transfer effect. analysis was to be made of the liquid products, that is, Heretofore it has generally been assumed that glycols those not appreciably volatile or quite soluble in the arise froin the combination of two alcohol free radicals, alcohol, irradiations were carried out with a 3 Mev. while carbonyl conipounds arc the result of the nrolecuVan de Graaff Accelerator employing much larger total Iar elimination of hydrogen, If these mechanisms are doses, while for those samples on which gaseous prodessentially correct, implying that the sole fate of the ucts were determined a cobalt-60 source was used. Clear, glassy samples were readily obtainable for all radicals is glycol formation, one would expect that high L.E.T. radiation would favor glycol formation, alcohols except, t-butyl alcohol. Thus the results obtained froin t-butyl alcohol in the solid state are not ( 5 ) IT. R XcDonnell and A. S. Newton, J . Am. Chem. Sac., 76, 4631 strictly coniparable with the others since, as has been (1954). COSDE.NSED PRUDCeTS
FROM ISOPROPYL ALCOHOL
---__
---
RADIOLYSIS
RADIATION cHEMIS$Rkk
April, 1g63
while in the case of the relatively lower concentrations of free radicds provided by y-rays the yield of glycol would be rehtively lower. Examination of 'Table IX reveals that iii the case of TABLE IX 100 e.v. Yields--------
